The present invention relates to a startup range neutron monitoring system for monitoring the output of a nuclear reactor at the time of starting up the nuclear reactor. More particularly, the invention relates to an apparatus for inspecting and testing the operating characteristic of a startup range neutron monitoring system.
FIG. 3 shows a conventional startup range neutron monitoring system. The startup range neutron monitoring system shown in FIG. 3 includes a startup range neutron monitor (SRNM) detector 1, an SRNM preamplifier 2, and a monitor 3. The SRNM detector 1 measures any neutron flux existing in the pressure vessel provided in a nuclear reactor. The SRNM preamplifier 2 receives the electric signal from the SRNM detector 1 and amplifies the signal. The monitor 3 receives the electric signal from the SRNM preamplifier 2 and acquires necessary information from the signals, thus monitoring the output power of the nuclear reactor.
The monitor 3 includes a pulse measurement unit 4, a Campbell measurement unit 5, a signal sorting unit 13, an arithmetic processing unit 6, a display unit 14, a diagnosis unit 15, an output unit 7, and a voltage setting unit 9. The pulse measurement unit 4 has discrimination-voltage setting unit 8 that sets voltage of a specific value. The pulse measurement unit 4 counts any pulse of a voltage higher than the voltage set by the discrimination-voltage setting unit 8. The Campbell measurement unit 5 measures the mean square value of pulsation at a frequency band of the electric signals output from the SRNM preamplifier 2. The signal sorting unit 13 sorts the electric signals from the SRNM preamplifier 2, some to the pulse measurement unit 4 and the others to the Campbell measurement unit 5. The arithmetic processing unit 6 calculates the output power of the nuclear reactor from the information supplied from the pulse measurement unit 4 and Campbell measurement unit 5. The display unit 14 displays the result of the calculation performed in the arithmetic processing unit 6. The diagnosis unit 15 diagnoses the other components of the monitor 3, for abnormality, if any, developing in the other components. The output unit 7 outputs the result of the calculation performed in the arithmetic processing unit 6, to an external apparatus. The voltage-setting unit 9 sets a high voltage, which will be applied to the SRNM detector 1.
The arithmetic processing unit 6 has a CPU, which generates instructions. The unit 6 gives these instructions to the other components and collects data items from the other components, through a bus 16. The arithmetic processing unit 6 has a function of testing the characteristics of the startup range neutron monitoring system. The unit 6 determines, when necessary, the discrimination characteristic and Plateau characteristic of the startup range neutron monitoring system. This function is implemented by using software, as one of the various functions of the startup range neutron monitoring system.
A radiation sensor exhibits an output-current characteristic with respect to the voltage applied to it. The output-current characteristic is generally called Plateau characteristic. Further, the radiation sensor exhibits one neutron-pulse sensitivity when the radiation contains gamma rays, and another neutron-pulse sensitivity when the radiation contains no gamma rays. The sensitivity characteristic due to the gamma rays is known as discrimination characteristic. Startup range neutron monitoring systems of the type described above are disclosed in, for example, the following references: Japanese Patent Application Laid-Open Publication Nos. 04-29085, 08-201526 and 2002-111654, the entire contents of which are incorporated herein by reference.
In the conventional startup range neutron monitoring system described above, the arithmetic processing unit 6 determines the discrimination characteristic and Plateau characteristic based on the software installed in the monitor system. This software cannot be separated from the other arithmetic operation functions. Hence, even if a part of the software is altered, the whole monitor system must be tested for characteristics and be verified for reliability and safety.
If only those parts of the software, which describe the function of determining the discrimination characteristic and Plateau characteristic, fail to work, they may adversely influence all arithmetic operation functions the arithmetic processing unit performs, because they cannot be separated from the other arithmetic operation functions.